rtc: Staticize non-exported __rtc_set_alarm()

It's not referenced outside this file so there's no need for it to be in
the global namespace and sparse warns about that.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>

drivers/rtc/interface.c

@@ -318,7 +318,7 @@ int rtc_read_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
 }
 EXPORT_SYMBOL_GPL(rtc_read_alarm);
 
-int __rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
+static int __rtc_set_alarm(struct rtc_device *rtc, struct rtc_wkalrm *alarm)
 {
 	struct rtc_time tm;
 	long now, scheduled;